In recent years, computers and the environment surrounding computers has been rapidly expanding. Together with such expansion, technology using computers is widely used and has become commonplace so that these days computers can be seen in every aspect of our daily lives.
Within this expansion of the environment surrounding computers, technology related to virtual reality is also expanding. The increasing speed of computers has made it possible to bring the construction of complicated virtual environments to even greater heights. Currently, this virtual reality technology has come to be used in various fields, and objects realized in virtual worlds are wide-ranging from large scale to small scale and high definition, such as outer space, metropolitan areas, environments in nature, manufactured products, internal organs, small animals, cells, and atoms. Moreover, not only is it being used for that which actually exists and can be actually seen, but also it is being used to visualize temperature distribution, airflow, and electromagnetic fields, which cannot actually be seen.
Amazing expansion has been attained in three-dimensional image display technology used to achieve such virtual reality, and utilization thereof ranging from installations at expositions or use for amusement purposes, to applications in the fields of education and medicine and applications in the various design, CAD/CAM, and measurement fields deserves our attention.
Techniques of displaying three-dimensional images are generally classified into a technique where a stereoscopic image is formed using an appropriate method and having the viewer of such image view it without assistance, and a binocular disparity technique devised so that, instead of a stereoscopic image, a right-eye view and a left-eye view of a flat image is formed and the right-eye view is viewed by the right eye and the left-eye view is viewed by the left eye. Typical examples of the former include holography and integral photography, and the latter includes three-dimensional movies where polarized glasses or liquid crystal shutters are used, and three-dimensional television using lenticular film.
These techniques of forming three-dimensional images, as typified by holography, still have unresolved technical issues preventing full color, high resolution, and real time viewing.
The binocular disparity technique is based on ergonomics, and provides three-dimensional images giving an enhanced ‘real’ feeling, and superior immersion and sensory feelings. However, it is not possible to freely change the viewpoint from which the three-dimensional object shown is viewed to coordinate with the user's movements using this technique by itself.
A method which modifies the three-dimensional image in accordance with the viewpoint and position of the viewer, a device (e.g., magnetic sensors or the like) worn for measuring the position of the head (viewpoint) of the viewer plus the binocular disparity technique allows the three-dimensional image to be viewed relative to the viewpoint position. However, with this technique, the number of users for which viewpoint movement within real-space can be reflected in the virtual world is limited to one person for each display. There is no display method appropriate for a plurality of viewpoints when a plurality of users shares a common display.
There are methods of performing time divided display for the number of users (for example, refer to MIYASATO, Tsutomu, et al., General Conference of the Institute of Electronics Information and Communication Engineers, A 16-21, 1997, or Japanese Patent Application Laid-open Hei 10-260377) and methods of driving display devices corresponding to the number of users in response to viewpoint position (for example, refer to KIMURA, Katsuyuki, et al., Conference on Three-Dimensional Imaging, 5-7, 1994). However, with the former, as the number of viewers increases, the allowable lower frequency limit of the composition of the three-dimensional view is not reached (the number of frames decreases), the display frequency is in inverse proportion to the number of users, which cause problems such as flickers to occur. With the latter, the number of display devices matching the number of users or a large-scale device is required, which is problematic in terms of price.
Thus, conventional devices for three-dimensional display of images and video have primarily come to use methods which display video for the right eye and video for the left eye using time division, and viewing is performed by putting on special glasses which open/close windows for the right and left eyes synchronous with the timing of this switching. In this case, the viewer is able to view the video via a screen from any position without distortion caused by that viewpoint positioning.
However, if a plurality of people try to view the same three-dimensional video without distortion, since the display switches back and forth between the right eye and left eye video of a plurality of positions, the time interval between displaying an image for each person that has increased the number of time divisions becomes longer, causing a flicker to be sensed.